Add regex to match Gnome and KDE calendar user-agents, for propagating calendar subscriptions

[msrn]

Refers: #17754
This pull requests adds Gnome Calendar/Evolution and KDE PIM/Akonadi calendars to the list of user-agents in WebCalCaching -plugin, and exposes subscribed calendars to these calendar clients.

User-agent of Gnome Calendar/Evolution
Evolution/3.40.3

KDE PIM/Akonadi user-agent
Mozilla/5.0 (X11; Linux x86_64) KIO/5.86 akonadi_davgroupware_resource_1/5.18.2 (21.08.2)

[tcitworld]

As per the comment above « calendar user agents that do not support subscriptions on their own », this doesn't look very right to me, as Evolution supports subscriptions, it just lacks subscription discovery for automatic configuration. We intentionally don't expose cached subscribed calendars for every calendar user agent because of performance reasons, it will be far better if every client lists the subscriptions and configures them manually (as of today, I think only DAVx⁵ does it properly).

I thought that KOrganizer or Kalendar supported adding manual calendar subscriptions, but it doesn't seem so, is that correct @CarlSchwan?

So KIO would be acceptable but instead of adding Evolution as well, I'd file a bug against https://gitlab.gnome.org/GNOME/evolution/-/issues to ask for subscriptions discovery.

For reference, this is the issue discussing the topic #17754

[CarlSchwan]

Yeah we don't support calendar subscription in Kalendar. Currently, we only support fetching a remote file one time when configuring the resource but we don't monitor for change. That wouldn't be too complex to implement I think but #notEnoughtTimeTooMuchTodo I created https://invent.kde.org/pim/kalendar/-/issues/206 to keep this in mind

[JackRoublard]

We intentionally don't expose cached subscribed calendars for every calendar user agent because of performance reasons, it will be far better if every client lists the subscriptions and configures them manually (as of today, I think only DAVx⁵ does it properly).

I understand the performance concerns, however as mentioned in #1497 there are also privacy concerns supporting the decision of adding even clients that do support subscriptions - not to mention that to those users who turned to self-hosting especially for the sake of being as independent and self-contained as possible, this approach just makes more sense.

Why not simply leave this tradeoff for every nextcloud admin to figure out ? The way I see it, the optimal solution could be as basic as checkboxes in the admin settings UI.

[msrn]

(as of today, I think only DAVx⁵ does it properly).

I think it is going to stay that way for a while. Looks like clients really don't care about adding this feature.

as Evolution supports subscriptions, it just lacks subscription discovery for automatic configuration

Window calendar also supports subscriptions, but lacks the Nextcloud specific subscription discovery. PR regarding for that was accepted but not for these clients, why?

[Vivida1]

Would be nice, or at least give the option to manually enable user-agents.

[msrn]

(as of today, I think only DAVx⁵ does it properly).

I think it is going to stay that way for a while. Looks like clients really don't care about adding this feature.

as Evolution supports subscriptions, it just lacks subscription discovery for automatic configuration

Window calendar also supports subscriptions, but lacks the Nextcloud specific subscription discovery. PR regarding for that was accepted but not for these clients, why?

Would still be nice to have reply to latter question.

[skjnldsv]

I was a bit too fast, sorry @msrn :)

Window calendar also supports subscriptions, but lacks the Nextcloud specific subscription discovery. https://github.com/nextcloud/server/pull/27488regarding for that was accepted but not for these clients, why?

I think it's a valid question. I see no reason we would accept one and not the others. 👍

[skjnldsv]

Rebase fail?
@msrn can you open a new PR maybe?